High-temperature members for use in high-temperature environments, such as moving blades, stationary blades, and combustors of gas turbines for power generation and jet engines, have thermal barrier coatings (TBCs) applied to their substrate surfaces in order to protect substrates made from metals from high temperatures. Thermal barrier coatings are composed of a metal junction layer formed on the substrate by low-pressure plasma spraying or the like and a ceramic layer formed on the metal junction layer by atmospheric plasma spraying. Materials including rare earth stabilized zirconias such as yttria-stabilized zirconia (YSZ) are used for the ceramic layer.
If damage, such as fracture or exfoliation, to the ceramic layer of a thermal barrier coating occurs during operation of a machine component such as a turbine or a jet engine, the temperature of the metal substrate of the high-temperature member rises, leading to breakage of the machine component. Therefore, it is necessary to determine the durability and remaining lifetime of the ceramic layer of the thermal barrier coating before or during operation of the machine component. To determine the durability and lifetime of a thermal barrier coating, a high-temperature member can be heated at use temperature for the use time; however, this is not realistic because a prolonged period of time is required to obtain test results. For this reason, a process of obtaining long-term test results by extrapolating from short-term test results using the Larson-Miller parameter is performed.
Patent Citation 1 discloses a method for estimating the temperature of a ceramic layer as a physical property that is useful for a durability assessment or a remaining lifetime assessment of a ceramic layer. Specifically, the surface temperature of the ceramic layer is estimated by substituting into a characteristic diagram showing the relationship between the area ratio of gap-like defects (stratified formation defects) and the value of the Larson-Miller parameter, obtained using a sample having the same composition as the ceramic layer, a measured value of the area ratio of gap-like defects in a cross section of a ceramic layer in a depth direction when the real machine has been used for a predetermined period of time.
Patent Citation 1: Japanese Unexamined Patent Application, Publication No. 2003-4549